The design of tactile thematic symbols.
Thematic maps are cartographic representations of themes, such as population or income. These types of maps can show information about specific locations, give general information about spatial patterns, and be used to compare the patterns on two or more maps (Slocum, McMaster, Kessler, & Howard, 2005). The importance of this cartographic method is evident in the sheer volume of scholarly papers and books on thematic mapping that provide guidelines that inform both the theoretical and design components of making these types of maps for sighted map users. Research has focused on creating tactile map symbols and formalizing the techniques in tactile mapping, including the articulation of good practices (Tatham, 2003). However, the development and use of symbols for static tactile thematic maps has not been studied extensively. The lack of attention is not due to the absence of need, however; researchers and practitioners have expressed a clear need for the development of effective tactile thematic maps (Lobben, 2005).
Even though thematic mapping has been a popular cartographic method for nearly 200 years, we cannot directly apply knowledge of the design of symbols for printed thematic maps as a guide for the creation of tactile symbols, given that it is often inappropriate to translate print map symbols into a tactile map format (James, 1982; Klatzky & Lederman, 1987). But, as we discuss later, several principles of cartographic design may be shared between the thematic design of tactile and visual symbols, such as max-contrast symbolization (Cromley, 2005; Dougenik & Sheehan, 1975; Gilmartin & Shelton, 1989), half-toning (Slocum, 1999), and nonlinear assumption (Kimerling, 1985). In the study presented here, we borrowed and applied these guidelines for making traditional print thematic maps to the design and subsequent evaluation of tactile thematic maps.
A primary goal of the research was to identify effective symbols for tactile thematic maps. An effective symbology is based on discriminability and the extent to which the symbols foster spatial understanding. The two research questions that drove the experimental design and data analysis were these:
1. Can the tactile map user discriminate among the different fill patterns that are used to represent distinct classes of maps?
2. Can these symbols be used to create a classed quantitative choropleth tactile map that facilitates the recognition and overall understanding of spatial patterns, such as the population distribution of a state?
Symbolization and use of tactile maps
A critical area of research in tactile mapping involves the legibility and meaningfulness of tactile symbologies (Lambert & Lederman, 1989). The reading of tactile maps consists of a series of processes, beginning with the discrimination and identification of symbols (Perkins, 2002). Early studies of legibility included those on the effect of noise in detecting point symbols (Berla & Murr, 1975); minimum sizes for areal and point tactile symbols (Nolan & Morris, 1971); and the identification of one symbol among a series of symbols of the same class, either points, lines, or area (Barth, 1982). Barth, along with others (Gill & James, 1973; Lambert & Lederman, 1989), used a matching task or a paired comparison task in which a single symbol was identified among a set. These studies are relevant because they mimicked behavior that would be performed with a map legend. However, they failed to test for context or to identify how symbols are interpreted when experienced in conjunction with other symbols and in real maplike layouts.
More recent research on the creation and detection of symbols has expanded from the analysis of simple legibility to the study of which environmental features are most important to symbolize (Lobben & Lawrence, 2011; Rowell & Ungar, 2003b; Siekierska & Labelle, 2001), the best production methods (Jehoel, Ungar, McCallum, & Rowell, 2005; Pike, Blades, & Spencer, 1992; Rice, Jacobson, Golledge, & Jones, 2005; Rowell & Ungar, 2003a), the standardization of tactile symbols (Rowell & Ungar, 2003a), and how symbols are cognitively processed and used (Jehoel, McCallum, Rowell & Ungar, 2006; Ungar, Jehoel, McCallum, & Rowell, 2005). With these studies in mind, a clear gap exists in the literature concerning the interpretation and testing of thematic map symbols in a whole-map context, particularly with regard to the recognition of spatial patterns.
To improve the design of tactile maps and symbols, it is critical to consider the psychological processes that are necessary to read tactile maps effectively. Jehoel et al. (2006) referred to this process as "cognitive tactualization," a practice that is comprised of two processes. One process is perceptual, involving the perception of the tactile stimuli or the receptors on the fingertips that allows the information to be perceived. The other is cognitive and entails the cognitive processes that transform the response to the tactile stimuli into information that a tactile map user can interpret.
From a perceptual standpoint, some tactile guidelines do exist that help guide the physical production of tactile images, including maps. For example, Braille Authority of North America (2010) has produced guidelines to inform the design of tactile graphics. These guidelines address issues of proximity (a minimum distance between tactile objects of at least .25 inch), prominence (reserve the most prominent symbols for the most important features), and hierarchy (graphics should demonstrate a conceptual or tactile hierarchy). Experimentally based guidelines have been produced as well (Bentzen & Peck, 1979; Grant, Thiagarajah, & Sathian, 2000; Hughes & Jansoon, 1994; Loomis, 1981). However, Jehoel et al. (2006) argued that the perceptual studies, or psychophysical studies, have focused more on a sensory-motor perspective. Although this research has been critical to understanding how to design tactile surfaces for legibility, the results have not informed the extent to which the tactile surfaces enhance understanding. Ultimately, understanding is the overall goal of information graphics (including maps), and to read a tactile map effectively, a user must be able to discriminate and organize the symbols into a meaningful representation of spatial data.
Cognitive studies of the use of tactile maps have investigated several topics, such as how geographic information is gathered from tactile maps (Espinosa, Ungar, Ochaita, Blades, & Spencer, 1999; Ungar, Blades, & Spencer, 1995), which map-reading strategies are used (Blades, Ungar, & Spencer, 1999; Perkins & Gardiner, 2003; Ungar, Blades, & Spencer, 1997), and how tactile maps aid in navigation (Loomis et al., 1993; Perkins, 2002). The study presented in this article contributes to the literature by combining the legibility of thematic tactile symbols with the effectiveness of a user' s ability to recognize the relevant spatial patterns presented on maps.
Design of thematic maps
A common thematic map, and the type used in our research, is a choropleth map. A choropleth map is one in which the data or enumeration units are represented by patterns or colors. In the case of a quantitative choropleth map, data classes are statistically created and represented by symbols, or colors, that are proportionate to the measurement of the statistic. When designing a choropleth map, the cartographer must make decisions about both the symbology and classification method, and often one affects the other. For example, if a cartographer chooses to represent the population of the 50 United States and chooses a simple classification method, quantiles, the states may be divided into five classes of 10 states. The result is five different symbols that need to be created, such as five shades of blue. However, if the cartographer chooses another method, natural breaks, the states may be divided into seven classes with a nonuniform distribution of states within each class. The result is seven different symbols, such as seven shades of green. Therefore, the design of the symbols for choropleth maps usually lies in the symbolization of the data classes. Moreover, because the data can be classified using different methods, a different number of classes may result. In our research, we focused on testing the effectiveness of three different class symbol schemes, allowing us potentially to identify more than one symbology for tactile thematic maps.
The design and production of choropleth maps are relatively streamlined because of well-established data-symbolization techniques. In addition, several studies have investigated how sighted people interpret and use these thematic map symbols (Board & Taylor, 1977; Crawford, 1973; Cromley, 2005; Dent, 1972; Gilmartin, 1981; McEachren, 1982). This type of research borrows three commonly applied methods of designing symbols for print thematic maps--the maximum-contrast method, the halftone technique, and the nonlinear assumption--to guide the creation of tactile thematic symbols. These methods are applied to ensure the maximal difference among symbols (the maximum-contrast method), the development of discrete or individual symbols (the halftone technique), and the perceptual class distinctions (the nonlinear assumption).
The maximum-contrast method is applied to ensure that each class shade is selected to be maximally different from one another. It optimally maximizes the perceptual gradients among classes by developing a consistent perceptual difference (increase or decrease) among consecutive classes (Cromley, 2005; Dougenik & Sheehan, 1975; Gilmartin & Shelton, 1989). We applied the maximum-contrast method in our study as a basis for exploring and ensuring optimal tactile acuity, which provides a smaller range of spatial acuity than the visual field (Golledge, 1993). Blades et al. (1999) noted that map users with visual impairments may have greater difficulty encoding information from a tactile map; as a result, we argue that map users must be able to distinguish among the classes easily, therefore spending their cognitive efforts interpreting the spatial distribution of data.
We borrowed the halftone technique for the design of the individual symbols. In designing symbols, three visual variables may be manipulated to create the class symbols on a printed map: hue, saturation, and value. Hue refers to the color, for example blue versus red. Saturation is the intensity of the color, the level of pure color versus gray, and value is the lightness or darkness. The combination of various psychological effects and physical phenomena affect one's perception of color.
Since tactile symbols cannot manipulate hue, saturation, and value directly, the halftone technique is applied. The halftone technique simulates continuous color values using ink dots and varying either their size or their spacing (Slocum, 1999). The resulting effect is a perceptually smooth transition from light to dark. In relation to the current research, we adapted this technique by changing the spacing of the tactile dots or creating more "lightness" or "darkness."
Thematic maps are often symbolized with a ramp of one color, such as a series of gray tones. Most printed maps are not perceived in such a way that the tones vary from light to dark in a perfect, linear correspondence with the physical stimulus or the percentage of the area that is inked. Rather, gray tones are interpreted in a graded series on the basis of what the user perceives as a smooth transition from one class to another (Kimerling, 1985). Therefore, the nonlinear assumption applies, which assumes that the perception of smooth transitions among classes is not based on set linear progressions. We applied the same assumptions in our study to the design of class symbology on a tactile choropleth map. Thus, tactile fill symbols for choropleth maps may need to be created with maximum differences among them and with nonlinear steps between the number of dots included to make up each fill pattern.
DESIGN AND PRODUCTION OF THE TACTILE MAPS
The thematic maps we created were produced on microcapsule paper. This choice was based on two previous findings. In comparing the effect of different raised-relief production methods, Jehoel et al. (2006) found that a search task was performed fastest by graphics produced on microcapsule paper. A further consideration was that microcapsule paper is the most commonly used raised-relief production method in private and public schools (Lobben, 2005; Rowell & Ungar, 2003a).
Tactile fill symbols were produced in ArcMap, a cartographic software package that is used extensively to analyze geographic data and produce visual maps. By using ArcMap, we accomplished two goals: First, the fill symbols that were created could be made and used successively on many maps with different themes; second, these symbols could be replicated easily by others.
ArcMap provides cartographic flexibility in creating unique map symbols. In the research, we used the Fill Editing Tool to make the tactile symbol fills, each of which was composed of random dots. Random dots were chosen to create the feel of an overall fill pattern, preventing users from counting the number of dots or searching for a preexisting pattern within the fill as a way to distinguish between fills or categories. The design of the class symbols was based on the number and space of dots for each fill. Again, borrowing from the half-toning technique, we produced smooth transitions between classes by controlling the spacing of the dots. We manipulated the spacing between the dots to create tactilely different classes, but maintained a consistency in the size of each dot in the fill. The goal was to create a series of classes that easily transitioned from one to the other, maintaining a cohesive, similar fill effect.
The final series of maps represented actual populations by county in three states: Arizona, Oregon, and Wyoming. The three states were chosen because they are approximately the same size geographically, similar in geometric shape, and contain a similar number and size of counties. In addition to investigating the extent to which our augmented halftone technique could be used to create tactilely distinctive classes on choropleth maps, we investigated the number of different tactile classes the participants could distinguish. In the production of printed or visual tactile map classes, guidelines suggest that a map reader can distinguish and remember four to seven different class symbols (Slocum, 1999). Considering differences between visual and tactile acuity, we included, as a baseline, maps that represented populations with two, three, and four classes in each of the three states. The map series included 30 maps, with each of the three classifications represented in each state at least three times.
ARCMAP TECHNICAL SETTINGS
Although the dot spacing patterns were random, we used specific and systematic technical settings to create each pattern. To manipulate the symbol fills, we used the Symbol Property Editor tool in ArcMap. Within the Symbol Property Editor tool, a marker fill symbol is used. This setting produces a fill symbol that is made up of points. These points are set to be generated in a random pattern. The dots that make up the fills are in a 3-point size. The borders are a 3-point line weight. The separation between the points can be set manually. The first class on all the maps is represented by a symbol with no fill. The second class is represented by a separation setting of x = 60.0, y = 60.0; the third class is x = 25.0, y = 22.0; and the fourth class is x = 5.0, y = 12.0. The linear measurement system is set to pixels.
Twelve participants were recruited for the experiment, six men and six women who ranged in age from 25 to 54, with an average age of 41. Each participant was a dog guide user, and either totally blind or significantly visually impaired.
The study followed the appropriate human subjects and informed consent procedures. It was approved by the Office of Protection of Human Subjects at the University of Oregon. Each participant was tested individually at a table in the public lobby of a hotel. Following the consent procedure, the researcher explained to each participant what a choropleth map was and how a tactile choropleth map could be produced with a different number of classes. Once the participants indicated that they understood these concepts, they were then given a tactile legend. This legend included a series of boxes that contained the fill patterns applied for each of the classification schemes, that is, two, three, and four classes. After the participants indicated that they understood the legend, the task questions presented next were reviewed until the participants verbally indicated that they understood the tasks.
Each of the 30 tactile maps was shown one at a time. For each of these maps, three questions were asked: (1) Can you find a county that contains this symbol? (an example of the fill symbol that was shown on the map was highlighted in a box to the side of the map), (2) How many different classes can you detect on this map? and (3) Can you describe the population distribution pattern of the map? Therefore, three types of maps, split by classes, and 10 questions per participant for each map type resulted in 120 responses per participant.
"Can you find a county that contains this symbol?" This question was answered correctly by all the participants on all 30 maps. A negligible time difference between class schemes was recorded. Across all the trials, the participants responded in an average of 16.6 seconds (SD = 13). The results by class scheme were further analyzed: Two classes yielded the fastest response at 14.7 seconds, and three classes yielded the longest response time at 18.5 seconds, while the response time for four classes was 16.6 seconds.
"How many different classes can you detect on this map?" More variability was observed in the participants' answers to Question 2. The highest percentage of correct answers was recorded for the maps containing two classes, at 87.5%, followed by the maps containing four classes, at 69.4%, with the lowest accuracy recorded for the maps containing three classes, at 59.3%. A similar, although not identical, pattern of response time was observed. Again, the quickest answers were for the four-class maps at an average of 24.3 seconds, followed by the two-class maps at 25.8 seconds, while three-class maps again took the longest at 31.6 seconds (SD = 16). Across all 30 maps, the average response time was 27.2 seconds.
"Can you describe the population distribution pattern of the map?" All the participants effectively described the spatial distribution for each map on all the trials. The response time was not recorded for this question because individual responses and the resulting times were likely mitigated by the participants' articulation styles (that is, how verbose the different participants were).
At this time, little research has been conducted on the creation, production, and comprehension of tactile thematic maps. To guide the research, we used some of the guidelines that guide the design and production of printed, visual thematic maps. In general, applying map-production guidelines for printed maps to the production of tactile maps should be exercised with caution. Tactile maps contain less information, use rigorous spacing rules, have fewer overall symbols from which to choose, and use markedly different printing methods. But in the case of thematic maps, the results of the study indicate that using the half-toning technique in conjunction with the maximum-contrast concept may provide effective crosscutting guidelines for the creation of tactile choropleth fill symbols.
The results showed that all the participants could correctly match each fill symbol, as displayed on a key, to counties of the same fill, or data class, on all the maps. These results suggest that the choices of the designs of the symbol fills that were used in the project led to accurate identification, and thus perception, of all the fill symbols. The participants demonstrated a resolute understanding of the sensory information provided by the tactile symbols. Each separate fill was distinct enough from its counterparts to facilitate infallible distinction. In addition, as we mentioned earlier, a different number of classes may be displayed on different maps. As a result, flexibility in the number of classes and corresponding symbology is required. This research has demonstrated that two, three, and even four classes of tactile thematic choropleth symbols can be created, are discriminable, and lead to an understanding of the overall distribution of spatial data.
Although seemingly simple, using a map key or legend is a critical component of map reading. Without a key, the map graphic contains only data on location; it simply shows where something is. But with the inclusion and use of the key, the map reader gains attribute data, or an explanation of what and how the geographic information is being displayed. The key, and, more important, the application of the key, to the mapped information provides an intersection of perception and cognition. The symbols are tactilely perceived and then the key provides information to attach cognitive meaning to them.
In the case of thematic maps, the key provides the user with the data values or classes that are connected with the patterns displayed on the map. With choropleth maps, the goal often is to use shades of color to show differences in the magnitudes of a variable, thereby displaying the geographic distribution of a phenomenon. This research has demonstrated that tactile "shades of color" can be designed and displayed so that users of tactile maps are able not only to decipher each class perceptually, but to locate the areas on the map that contain that symbol.
The symbols that we designed for the study were used in a whole-map context, and the symbols were presented using realistic map stimuli. It is important to present symbols in the context of other symbols to determine their legibility, since symbols that are presented in a simple paired comparison test do not always yield the same level of discrimination. The results of the study demonstrate that all the symbols are identifiable when they are presented together. The next step for the map reader is to put the information together, to tell a story, or, in this case, to describe the population distribution within the three states.
With regard to Question 3, all the participants effectively described the spatial data patterns displayed on all the maps, no matter how many classes were present. All the participants could correctly identify, by matching, the thematic map symbols presented on the tactile maps. The results revealed variation in how well the participants could identify the number of classes on each map, but that difference did not influence their ability to describe the spatial data patterns with accuracy. These results suggest that although the participants could not determine the number of classes on each map every time, the overall magnitude patterns were easily discriminable and identifiable. The participants consistently and readily understood the difference between relative spatial data-distribution patterns or could identify that certain areas on the map, as represented by the tactile symbols, had higher or lower population numbers.
The maps designed for the study represented population distribution data using choropleth maps, which is a popular type of thematic map, and one that many people have encountered. But because few, if any, tactile versions of these types of thematic maps exist, the results were likely not influenced by the participants' previous experiences with similar map sets or with thematic maps in general. Instead, the results suggest that the map symbols that we created led the participants to obtain, interpret, and use the information on the maps effectively.
The study showed that discriminable and effective thematic tactile maps with classed data can be produced. The participants were able to recognize and describe spatial patterns shown on thematic maps that were designed with the symbol-creation guidelines discussed here. These results mirror previous results, conducted with sighted map users, which suggest that readability is more efficient with effective thematic symbolization (Crawford, 1971). Therefore, the tactile map symbols that were used in the research may have aided the perceptual uptake of the map information, leading to successful descriptions of the spatial distributions shown on the maps. In other words, cognitive skills, such as the discrimination of map elements (that is, lines, symbols, and textures), and the development of spatial relationships (that is, next to, between, and above) may have been eased by successful design techniques. Other cognitive skills, such as extracting meaning from the graphic, may have been enhanced by designing legible symbols because users are able to organize spatial map patterns before any meaning is attached to the symbolization.
Several areas within tactile thematic mapping can be explored further. First, only one method, choropleth, was used to create the tactile thematic maps that were used in the study. Other thematic mapping methods include proportional symbols, isarithmic, cartograms, and dot density. Second, thematic maps may also represent two or more variables, such as bivariate and multivariate maps. The study included only tactile thematic maps with one variable. Third, the study used microcapsule paper as a production method. Because production methods yield vastly different tactile surfaces, additional research could focus on thematic tactile symbols with other production methods, such as Thermoform.
Access to tactile thematic maps of both country-level and state-level patterns of socioeconomic topics, such as population, income, education, age, and gender, are important for understanding a county's culture and society (Lobben, 2005). The study reported here took the first critical step, which was to develop and study empirically the use of symbols that can be used to make tactile thematic maps. We did not intend to make suggestions of how these maps should be used in educational or rehabilitative settings or who should be using them, although it is apparent that there is need for further study in this area. But this research does demonstrate that map readers who are blind or have low vision can effectively use tactile thematic maps that are produced from the methods described here from both a perceptual and cognitive standpoint. The article has also provided guidelines, albeit preliminary, regarding the symbolization of tactile thematic maps made with microcapsule paper with two, three, and four classes.
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Megan M. Lawrence, Ph.D., research assistant, Department of Geography, University of Oregon, 1251 University of Oregon, Eugene, OR 97403-1251; e-mail: <email@example.com>. Amy K. Lobben, Ph.D., associate professor, Department of Geography, University of Oregon, Eugene; e-mail: <firstname.lastname@example.org>.
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|Author:||Lawrence, Megan M.; Lobben, Amy K.|
|Publication:||Journal of Visual Impairment & Blindness|
|Date:||Oct 1, 2011|
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